1. Field of the Invention
This invention relates to a silicon wafer used as a substrate for forming a semiconductor product such as a semiconductor device or a semiconductor integrated circuit device.
2. Description of the Related Art
Recently, as LSIs are formed with higher integration density and finer pattern, the requirement for the property of silicon wafers used as the substrates for forming the LSIs becomes severer. For this reason, in the pull-up stage of a silicon single crystal, the amount of impurity is reduced and the interstitial oxygen concentration is adjusted to a reasonable value, and in the processing stage, various improvements such as enhancement of flatness of the wafer are effected. As the result of this, the manufacturing yield can be enhanced to some extent.
However, even if a semiconductor device is formed by using the wafer thus improved, variation in the manufacturing yield which may be considered to be caused by the wafer itself occurs and the yield cannot be enhanced as a whole. This tendency can be frequently observed particularly when N-type wafers are used.